1. Field of the Invention
This invention relates to solid resinous products which are esters of hindered carboxylic acids. More specifically, the invention relates to solid ester products which have high degree of hydroxyl functionality.
2. Description of Related Art
Use of resins in diverse commercially important applications is well-established. The ability to prepare resins which have preselected properties has increased the acceptance of such materials in many applications. However, the physical form of some resins often makes them difficult to distribute in commerce. Many such resins are highly viscous liquids or gelatinous semi-solids, neither of which is conveniently transported. Resins having both a high proportion of hydroxyl functionality and a conveniently-transported physical form have not been made widely available.
Resinous compounds are useful, inter alia, in lacquers, waxes, and other protective coatings; for textile finishing treatments; and as binders for particulate matter. However, many resin products are difficult to prepare and handle.
Ester products having hydroxyl substituents made by the condensation of unhindered carboxyl-functional constituents with hydroxyl-functional constituents (polyols) are well known in the art. Such ester products are available from diverse sources. Examples of such products are those described in U.S. Pat. No. 2,488,303, which discloses the esterification of organic acids with glycols. However, these products do not provide the required combination of product characteristics such as ease in handling and desired high hydroxyl functionality.
One approach for increasing the hydroxyl functionality of ester products involves using a hydroxyl-substituted carboxylic acid for reaction with the polyol. However, the carboxyl group on such hydroxyl-substituted acids is often sterically hindered and esterification of such sterically hindered carboxylic acids is significantly more difficult than esterification of the unhindered carboxylic acids such as the esterification described in U.S. Pat. No. 2,488,303. Known techniques for the esterification of hindered carboxylic acid moieties typically require use of strong acid catalysts, so the variety of such esters is limited. Therefore, the ester products of sterically hindered carboxylic acids are not well known and not easily obtained.
Ungelled resins suitably cured by exposure to ionizing radiation or ultraviolet light are disclosed in U.S. Pat. No. 4,649,082. The resins comprise esters which are the reaction product of a polyfunctional hydroxy-containing carboxylic acid, a hydroxyl-functional compound, and an unsaturated carboxylic acid. The esters may be prepared in one- or two-step processes. In the latter, it is broadly disclosed that the polyfunctional hydroxy-containing carboxylic acid having a molecular weight less than 1000 (one example being dimethylolpropionic acid) can be reacted with an organic hydroxyl-functional compound, such as a diol, at a molar ratio of anywhere between about 3:1 to 0.5:1, preferably between 2:1 to 1.5:1, and at a temperature between about 150.degree. and 220.degree. C. Typically, an esterification catalyst, such as butyl stannoic acid, dibutyltin oxide, antimony oxide, dibutyltin dilaurate, paratoluenesulfonic acid, and methane sulphonic acid is utilized. However, the physical characteristics of these esters are not reported. In the illustrated examples, dimethylolpropionic acid is reacted with diethylene glycol, 1,4-butanediol, cyclohexanedimethanol, and dipropylene glycol, all at molar ratios of acid to polyol of 2:1. No information about the physical characteristics of the ester products is provided.
The self-condensation product of a polyhydroxymonocarboxylic acid is disclosed in U.S. Pat. No. 3,669,939. Small amounts of other such acids, monohydroxy compounds, monocarboxylic compounds, and polyhydroxy compounds also may be co-condensed but their presence is undesired. Only the self-condensation products of poly-functional (i.e., hydroxycarboxylic compounds) constituents are exemplified.
U.S. Pat. No. 3,441,953 discloses the esters of dimethylolpropionic acid with various ethylene glycols. Esters prepared at a 1:1 molar ratio of dimethylolpropionic acid with triethylene glycol (molecular weight 150) and with polyethylene glycol-300 (PEG 300-i.e., PEG having an approximate molecular weight of 300) are described as oily liquids. Using heavier PEG's yields products which range from pasty solids to waxy semi-solids which melt in one's hand.
It is an object of this invention to provide new esters of sterically hindered polyhydroxy monocarboxylic acids.
It is a further object of this invention to provide new esters of sterically hindered polyhydroxymonocarboxylic acids which provide a high degree of hydroxyl functionality.
It is another object of this invention to provide new esters of sterically hindered polyhydroxymonocarboxylic acids, which esters are sufficiently solid to be conveniently transported in commerce as prills, granules, powder, or in other durable forms.
It is yet another object of this invention to provide a method of preparing these esters.
It is a still further object of this invention to provide alkyd and polyester resins made using these esters.